Off-campus UMass Amherst users: To download campus access dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.
Non-UMass Amherst users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
Dissertations that have an embargo placed on them will not be available to anyone until the embargo expires.
Author ORCID Identifier
https://orcid.org/0000-0002-0848-2097
AccessType
Open Access Dissertation
Document Type
dissertation
Degree Name
Doctor of Philosophy (PhD)
Degree Program
Physics
Year Degree Awarded
2021
Month Degree Awarded
February
First Advisor
Lorenzo Sorbo
Subject Categories
Cosmology, Relativity, and Gravity
Abstract
We study the production of fermions through a derivative coupling to an axion inflaton and the effects of the produced fermions on the scalar and tensor metric perturbations. We show how such a coupling can arise naturally from supergravity with an axion-like field driving large-field inflation and small instanton-like corrections. We present analytic results for the scalar and tensor power spectra, and estimate the amplitude of the non-Gaussianties in the equilateral regime. The scalar spectrum is found to have a red-tilted spectral index, small non-Gaussianities, and can be dominant over the vacuum contribution. In contrast, the tensor power spectrum from the fermions is always subdominant compared to the vacuum contribution. The pseudoscalar coupling will favor production of one chirality of the fermions over the other, and therefore, it is expected that the resulting gravitational waves will be chiral. However, the parity-odd component of the power spectrum is shown to be subdominant to the parity-even component. The combined results of the scalar and tensor spectra allow to lower the energy scale of inflation, effectively lowering the tensor-to-scalar ratio. Chaotic inflation, in which the inflationary potential is quadratic, is currently ruled out as it predicts too large a tensor-to-scalar ratio. We show how this fermion-axion model can allow for quadratic inflation which agrees with all current measurements.
DOI
https://doi.org/10.7275/20618755
Recommended Citation
Roberts, Michael, "Phenomenology of Fermion Production During Axion Inflation" (2021). Doctoral Dissertations. 2134.
https://doi.org/10.7275/20618755
https://scholarworks.umass.edu/dissertations_2/2134